Management of Presentation Time in a Digital Media Presentation System with Variable Rate Presentation Capability

ABSTRACT

Techniques are provided for managing Presentation Time in a digital rendering system for presentation of temporally-ordered data when the digital rendering system includes a Variable Rate Presentation capability. In one embodiment, Presentation Time is converted to Data Time, and Data Time is reported instead of Presentation Time when only one time can be reported. In another embodiment, a predetermined one of Presentation Time and Data Time is returned in response to a request for a Current Time.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No. 10/919,963, filed on Aug. 16, 2004, entitled, “Management of Presentation Time in a Digital Media Presentation System with Variable Rate Presentation Capability,” which is hereby incorporated by reference; and which is a continuation-in-part of U.S. patent application Ser. No. 10/014,894, filed on Dec. 1, 2001, entitled “Management of Presentation Time in a Digital Media Presentation System with Variable Rate Presentation Capability,” which is hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to the field of content presentation by a digital rendering system such as a digital media player.

2. Related Art

Most traditional digital rendering systems, such as RealNetworks® RealPlayer® digital media players, maintain an internal variable during playback of media content that reflects a current presentation time (hereafter referred to as “Current Time”). Current Time is, in effect, a current “position” in the media content that is being displayed and rendered. Typically Current Time is set to zero at the beginning of the media content, and it reaches a measure of time equal to a duration of presentation of the content of the entire work when the end of the media content is reached.

In most traditional players, such as the RealPlayer® digital media player, a Current Time value is: (a) regularly calculated by a single module; (b) acquired and stored by core routines of the player; and (c) distributed to, and utilized by, various internal player objects. These internal objects utilize the Current Time value to determine when it is time to initiate or terminate various tasks associated with media content playback. The calculation of a Current Time value by the single module, and the distribution to, and utilization by, multiple objects within a player of the same Current Time value has a desirable result of keeping all objects synchronized.

Typically the Current Time value must be regularly and accurately updated by the player, or the presentation of media content will be faulty. For instance, if the Current Time value is not updated sufficiently often, a video component of a media stream may appear uneven or jumpy, and gaps in an audio content may be audible.

Although the concept of Current Time seems straightforward, in fact, it conflates two subtly different properties of media playback. The first property of media playback that is conflated in the concept of Current Time is a time elapsed since the beginning of the media content presentation (hereafter called “Presentation Time”). Thus, if the media has been playing for one minute, the value of Presentation Time is 60,000 milliseconds. All of time values discussed herein can be measured in various units. Two popular units are milliseconds, and centi-nanoseconds, or 1/10,000,000 of a second. The unit of measurement is not an issue here. Other considerations of representing time that are not issues here are the precision, the range of values, and the format of the representation.

The second property of media playback that is conflated in the concept of Current Time is a location in the media content stream that is currently being played (hereafter called “Content Time”). In a traditional linear media stream that is always played back at a fixed, “normal” rate, any given content element is always presented after a fixed amount of time has elapsed from the beginning of playback. Because of this, each such content element can be regarded as having a timestamp associated with it, i.e., a time value specifying how long it would take to reach that location, starting from the beginning of the media content, and playing at normal rate. Hereinafter we will call this property “Data Time.”

Presentation Time and Data Time are identical in traditional players, because traditional players can only present media content at a fixed “normal” rate. However, when a player is enhanced with a Time-Scale Modification (TSM) capability, it can present media content at various rates. Because of this, Presentation Time and Data Time are no longer the same. For example, if a 60-second clip of media content is presented at a fixed rate that is twice normal rate, at the end of the clip the Data Time is 60,000 milliseconds, but the Presentation Time is 30,000 milliseconds. This is because it only takes 30 seconds to play the 60-second clip.

We have discovered that problems may occur when a traditional player is enhanced with TSM functionality. In particular, if a Current Time value is distributed to multiple objects, some of them may interpret the Current Time value as specifying Data Time, some of them may interpret the Current Time value as specifying Presentation Time, and some of them may interpret the Current Time value as specifying both Data and Presentation Time. Thus, a first problem occurring when a traditional player is enhanced with TSM functionality is that the significance of the time value distributed to multiple objects is, in general, ambiguous. A second problem occurring when a traditional player is enhanced with TSM functionality is that Data Time does not, in general, equal Presentation Time, and the calculation, storage, and distribution of a single time value is inadequate to specify both values.

It is quite common for media players to rely on an audio renderer (for example, a player object responsible for outputting audio content through, for example, a computer sound card) to calculate and update the Current Time value. This is done because the nature of audio representation is such that typically each audio data element has either a fixed, or explicitly specified presentation duration, associated with it, and these presentation durations are enforced by audio rendering hardware. Therefore, the audio renderer can typically determine Presentation Time either by maintaining a running total of the presentation durations of all audio data elements rendered since playback began, or in some cases by querying the audio rendering hardware itself for the equivalent value.

If a media player does in fact acquire the Current Time value from the audio renderer, the value that the audio renderer will return to the system will typically be the Presentation Time. Since most of the rest of the system needs Data Time, most of the rest of the system can no longer employ the value returned by the audio renderer object.

As one can readily appreciate from the above, a need exists in the art for a method and apparatus for solving one or more of the above-described problems.

SUMMARY

Techniques are provided for managing Presentation Time in a digital rendering system for presentation of temporally-ordered data when the digital rendering system includes a Variable Rate Presentation capability. In one embodiment, Presentation Time is converted to Data Time, and Data Time is reported instead of Presentation Time when only one time can be reported. In another embodiment, a predetermined one of Presentation Time and Data Time is returned in response to a request for a Current Time.

In one embodiment of the present invention, a method is provided for rendering temporal sequence presentation data in a rendering system. The method includes steps of: (A) receiving a request from a first component of the rendering system for a first current time; (B) identifying a value of a presentation time parameter representing an amount of time elapsed during rendering of a portion of the temporal sequence presentation data; (C) providing the value of the presentation time parameter to the first component in response to the request; (D) receiving a request from a second component of the rendering system for a second current time; (E) identifying a value of a data time parameter representing an amount of time required to render the portion of the temporal sequence presentation data at a default presentation rate; and (F) providing the value of the data time parameter to the second component in response to the request; (G) wherein the presentation time parameter value and the data time parameter value represent different times.

In another embodiment of the present invention, a method is provided for use in a rendering system for rendering temporal sequence presentation data. The method comprising steps of: (A) initializing a presentation time parameter value to zero, the presentation time parameter representing an amount of time elapsed during rendering of a portion of the temporal sequence presentation data; (B) for each element in the portion of the temporal sequence presentation data, performing steps of: (1) identifying a default rendition period of the element; (2) identifying an actual presentation rate of the element; (3) dividing the default rendition period of the element by the actual presentation rate of the element; (4) adding the quotient of step (3) to the presentation time parameter value; and (C) identifying the sum produced by steps (A) and (B) as the presentation time parameter value.

In another embodiment of the present invention, a method is provided for use in a rendering system for rendering temporal sequence presentation data. The method includes steps of: (A) receiving an explicit request for a value of a presentation time parameter representing an amount of time elapsed during rendering of a portion of the temporal sequence presentation data, wherein the amount of time differs from an amount of time required to render the portion of the temporal sequence presentation data at a default presentation rate; and (B) providing the value of the presentation time parameter in response to the request.

In another embodiment of the present invention, a method is provided for use in a rendering system for rendering temporal sequence presentation data. The method includes steps of: (A) receiving an explicit request for the value of a data time parameter representing an amount of time required to render a portion of the temporal sequence presentation data at a default presentation rate, wherein the amount of time differs from an amount of time elapsed during rendering of the portion of the temporal sequence presentation data; and (B) providing the value of the data time parameter in response to the request.

In another embodiment of the present invention, a method is provided for enhancing a rendering system which renders temporal sequence presentation data, the rendering system not including distinct current presentation time and current data time parameters. The method includes steps of: (A) adding to the rendering system a monitoring module for monitoring values of a current presentation rate parameter that may vary over time, the current presentation rate parameter representing a current rate at which the portion of the temporal sequence presentation data is being rendered; (B) adding to the rendering system a data time module to identify, based on the values of the current presentation rate parameter, a current data time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at a default presentation rate; (C) adding to the rendering system a presentation rate modification module to render a portion of the temporal sequence presentation data at any of a plurality of presentation rates; and (D) adding to the rendering system a current time module for returning the value of a predetermined one of the presentation time parameter and the data time parameter in response to a request for a current time; wherein the presentation time parameter has a value that differs from the data time parameter value.

In another embodiment of the present invention, a method is provided for enhancing a rendering system which renders temporal sequence presentation data, the rendering system not including distinct current presentation time and current data time parameters. The method includes steps of: (A) adding to the rendering system a monitoring module for monitoring values of a current presentation rate parameter that may vary over time, the current presentation rate parameter representing a current rate at which the portion of the temporal sequence presentation data is being rendered; (B) adding to the rendering system a presentation time module to identify, based on the values of the current presentation rate parameter, a current presentation time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at the current rate; (C) adding to the rendering system a presentation rate modification module to render a portion of the temporal sequence presentation data at any of a plurality of presentation rates; and (D) adding to the rendering system a current time module for returning the value of a predetermined one of the presentation time parameter and the data time parameter in response to a request for a current time; wherein the presentation time parameter has a value that differs from the data time parameter value.

In another embodiment of the present invention, a method is provided for use in conjunction with a rendering system which renders temporal sequence presentation data. The method includes steps of: (A) receiving a request for a current time of the temporal sequence presentation data after a portion of the temporal sequence presentation data has been rendered by the rendering system; (B) in response to the request, performing steps of: (1) identifying a data time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at a default presentation rate; and (2) providing the data time parameter value in response to the request.

In another embodiment of the present invention, a method is provided for use in conjunction with a rendering system which renders temporal sequence presentation data. The method includes steps of: (A) receiving a request for a current time of the temporal sequence presentation data after a portion of the temporal sequence presentation data has been rendered by the rendering system; (B) determining, based on a property of the request, whether to return a value of a data time parameter or a value of a presentation time parameter; and (C) returning, in response to the request, the value determined in step (B).

In another embodiment of the present invention, a method is provided for use in conjunction with a rendering system which renders temporal sequence presentation data. The method includes steps of: (A) receiving a request for a current time of the temporal sequence presentation data after a portion of the temporal sequence presentation data has been rendered by the rendering system; (B) identifying an initial current time of the temporal sequence presentation data; (C) identifying at least one presentation rate associated with the temporal sequence presentation data; (D) modifying the initial current time based on the identified at least one presentation rate to produce a modified current time; and (E) providing the modified current time in response to the request.

In another embodiment of the present invention, a method is provided for use in conjunction with a rendering system which renders temporal sequence presentation data including a plurality of data samples. The method includes steps of: (A) grouping the plurality of data samples into a plurality of buffers; (B) associating with each of the plurality of buffers a corresponding presentation rate; (C) associating with each of the plurality of buffers a corresponding initial data time; (D) associating with each of the plurality of buffers a corresponding initial presentation time; (E) associating with each of the plurality of buffers a default rendition period; and (F) associating with each of the plurality of buffers an actual rendition period.

Other features and advantages of various aspects and embodiments of the present invention will become apparent from the following description and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a Presentation System embodied as a RealNetworks® RealPlayer® application running on a computer;

FIG. 2 shows a block diagram of a generalized Presentation system according to one embodiment of the present invention that includes Presentation System Controller Modules, other Presentation Modules (including a Presentation Rate Modification Module), and a number of Renderers;

FIG. 3A is a flowchart of a method for identifying values of presentation-related parameters according to one embodiment of the present invention;

FIG. 3B is a flowchart of a method for identifying a current Data Time based on a current Presentation Time according to one embodiment of the present invention;

FIG. 3C is a flowchart of a method for identifying a current Data Time based on a current element index according to one embodiment of the present invention;

FIG. 3D is a flowchart of a method for identifying a current Presentation Time based on a current Data Time according to one embodiment of the present invention;

FIG. 3E is a flowchart of a method for identifying a current Presentation Time based on a current element index according to one embodiment of the present invention;

FIG. 3F is a flowchart of a method for identifying an Unmodified Cumulative Rendition Period for an element and a Data Time at the beginning of the element according to one embodiment of the present invention;

FIG. 3G is a flowchart of a method for identifying a Modified Cumulative Rendition Period for an element and the Presentation Time at the beginning of the element according to one embodiment of the present invention;

FIG. 4 is a flow chart of a method for satisfying a request for a Current Time according to one embodiment of the present invention; and

FIG. 5 is a flowchart of a method for satisfying a request for a Current Time according to another embodiment of the present invention.

DETAILED DESCRIPTION

In accordance with one embodiment of the present invention, Presentation System 100 (a more general definition of a Presentation System is provided below) is embodied as a RealNetworks® RealPlayer® application running on a computer, for example, under some version of the Microsoft Windows operating system. As shown in FIG. 1, application module 110 sends to, and receives from, Player Core object 120, control and status messages such as, for example, Play, Pause, Stop, and so forth. Temporal Sequence Presentation Data, also referred to herein as Presentation Data, (a more general definition of Temporal Sequence Presentation Data is provided below) is embodied as streaming media content and is delivered to the RealPlayer® application over the Internet, a local-area network (LAN), or from files stored in the computer that is executing the RealPlayer® application. For example, in accordance with one embodiment, the Presentation Data, for example, audio data, is received by media content source module(s) 130, and are placed in audio media data buffers 140 that are made available to Player Core object 120.

As will be defined in more detail below, each data element of the Presentation Data has a Rendition Type that corresponds to a type of Renderer (a more general definition of Renderer is provided below) that can be used to render the data element. For example, for the embodiment described above, the Rendition Types that can be rendered include but are not limited to audio (encoded in various formats), video, still images, text, and scripts. In particular, audio is a Time-Distinguished Rendition Type (a more general definition of Time-Distinguished Rendition Type is provided below). As a result, for this embodiment, audio is organized within the RealPlayer® application in buffers that contain, for example, 100-milliseconds of sample values. Further, every buffer is timestamped, so these buffers are Timestamped Elements (as more generally described below, this means that the Data Time of the element is explicitly represented as part of the element), and the time associated with the first sample in every buffer is specified in milliseconds.

In accordance with this embodiment, the Rendition Period (as more generally described below, this is the length of time the rendering process should last for the element) of the audio buffers is 100 milliseconds. In some ways the individual audio samples play the part of the data elements as described below. It would be obvious to someone of ordinary skill in the art how to sometimes regard 100 millisecond buffers of samples and sometimes the individual samples themselves as audio elements. In accordance with this embodiment, a sample period of the individual audio samples is stored in a header that is part of the sample buffer definition (for example, one 10,000^(th) of a second is a typical sample period).

In accordance with this embodiment, an object called TSMAudioDevice object 150 combines functions of the Renderer for audio data (TSMAudioDevice Audio Renderer 160) and a Variable Rate Presentation Module (a more general definition of Renderer is provided below) (TSMAudioDevice VRP Module 170). In accordance with this embodiment, the audio Renderer part of TSMAudioDevice object 150 (i.e., TSMAudioDevice Audio Renderer 160) is a Timing Renderer (a more general definition of a Timing Renderer is provided below) for Presentation System 100. Note that the RealNetworks® RealPlayer® application does not include support for variable rate playback. However, Plug-In 180 comprises a product called a 2×AV Plug-In is available from Enounce, Incorporated of Palo Alto, Calif. When the 2×AV Plug-In is installed on a computer that has had the RealPlayer® application previously installed, it “plugs into” the RealPlayer® application, and adds variable rate playback capability thereto. The 2×AV Plug-In has its own User Interface, which includes a slider that a user can manipulate to adjust playback rate. In operation, the 2×AV Plug-In communicates with TSMAudioDevice object 150 by sending messages through an object called State Information Exchange Server 190 (“SIX Server 190”).

Thus, in accordance with this embodiment, TSMAudioDevice object 150 accepts messages from SIX Server 190 that specify a desired playback or presentation rate. Playback or presentation rate values can range from 0.3 to 3.0 (a rate of 1.0 is normal; a rate of 0.3 is 30% of the normal rate; and a rate of 3.0 is three times faster than the normal speed). TSMAudioDevice object 150 receives SIXExchange messages from SIX Server 190, and stores a requested playback rate value contained in these messages as a new value of an internal Current Presentation Rate parameter or property. In addition, as shown in FIG. 1, TSMAudioDevice object 150 receives buffers 200 of audio data to be rendered (i.e., played out through the computer's sound card) from Player Core object 120. When TSMAudioDevice object 150 receives buffers 200 of audio data to be rendered, it is processed by TSMAudioDevice VRP Module 170. TSMAudioDevice VRP Module 170 processes buffers 200 through a library of signal processing routines, for example, a suitable library of signal processing routines called the Time Scale Tailor package is available from Enounce, Incorporated of Palo Alto, Calif. In accordance with this embodiment, this library carries out digital signal processing procedures on buffers 200 of audio samples that has the effect of reducing the number of samples in the buffer (when playing faster than real time) or increasing the number of samples in the buffer (when playing slower than real time), thereby effectively changing the playback rate. For example, in accordance with this embodiment, processing the buffer using the library decreases or increases the samples in a particular way so as to leave the perceptual and linguistic information in the buffers unchanged, but to change the duration of the buffers. Additionally, playback rate parameters, unmodified and modified buffer lengths and Rendering Period values, and other time-related values are calculated by TSMAudioDevice VRP Module 170, and are stored with each audio buffer. Then, modified audio data buffers 210 are stored by TSMAudioDevice VRP Module 170 for presentation by TSM AudioDevice Audio Renderer 160. TSM AudioDevice Audio Renderer 160 comprises Audio Renderer Core Object 165 that submits modified buffers 210 for processing to the computer's audio electronics, for example, Computer Sound Card 220. For example, as shown in FIG. 1, Core Object 165 comprises an interface known as a WAV driver. This interface is defined by Microsoft, and is supported by the Windows operating system.

On a regular basis during playback or presentation, Player Core object 120 calls a method implemented by TSMAudioDevice object 150 called GetCurrentAudioTime( ). This method returns a Current Time in milliseconds. Additionally, every time a buffer of audio samples is processed (for example, buffer 200), TSMAudioDevice object 150 is responsible for calling a Player Core object 120 method called OnTimeSync( ), and passing to the Player Core object 120 method the Current Time in milliseconds. Player Core object 120 interprets both of these times as Data Times. In this embodiment, Presentation System 100 (other than TSMAudioDevice object 150) does not support the concept of Presentation Times that are different than Data Times. To do this, in accordance with one embodiment of the present invention, TSMAudioDevice object 150 carries out methods described below to convert Presentation Time (for example, as reported by its WAV driver Core object routines) into Data Time (as needed by Player Core object 120).

Before describing the methods to convert Presentation Time into Data Time, we present generalizations of the matters described above in conjunction with FIG. 2. In particular, FIG. 2 shows a block diagram of a generalized Presentation system that includes: Presentation System Controller Modules 400, Other Presentation Modules 410 (including a Presentation Rate Modification Module), and a number of Renderers, for example, Audio Renderer 420, Video Renderer 430, and Other Renderers 440. Further, as shown in FIG. 2, Temporal Sequence Presentation Data 450 is applied as input to Other Presentation Modules 410.

As defined herein, a Presentation System means a system or method that: (a) acquires, interprets, decodes, and manages presentation of Temporal Sequence Presentation Data (defined below); (b) selects, instantiates, initializes, controls, and monitors Renderers (defined below); (c) initiates a presentation by determining which presentation data elements are to be submitted first to which Renderers, effecting such submission, and causing the Renderers to begin processing; (d) maintains a Current Time parameter, whose value is regularly updated in a monotonically-increasing fashion during linear presentation (the value may be set to zero or any other value when presentation is stopped, or a jump is performed to a non-sequential location)—the Presentation System may maintain and update the value of the Current Time parameter by identifying a Renderer that can reliably maintain and update its Cumulative Rendition Period, and arrange to acquire the value of that parameter at regular intervals; (e) distributes its Current Time parameter to other Presentation Modules as needed; and (f) manages the presentation process, including by determining which data elements should be submitted next to which Renderers, and by comparing its Current Time value to the Data Time of those data elements, thereby determining when to effect such submission.

A digital media player is a common type of Presentation System, but there are many other types of Presentation Systems. For example, a controller that processes a script which causes digitally-controlled manufacturing equipment to make a printed circuit board is also a Presentation System, as is a controller that processes a script which causes a robot to perform a dance.

As defined herein, a Renderer is a system or method having the following characteristics: (a) the Renderer processes Temporal Sequence Presentation Data (defined below); (b) the Renderer processes data elements in an ordered sequence in which “earlier” elements are processed before “later” elements (the order may be determined by the order in which the elements are submitted to the Renderer, or by the Data Times (defined below) of the elements, or by using other techniques); (c) processing a data element takes a finite amount of time (possibly but not typically zero) known as the Rendition Period of the data element; (d) processing a sequence of data elements takes a finite amount of time directly related to the sum of the Rendition Periods of the individual elements, and, potentially, some other factors (the amount of time required to process (render) a sequence of data elements is called a Cumulative Rendition Period for those elements); and (e) at least one instance of a Renderer (often associated with rendering of audio data) has a capability of reporting back to a module, for example, a Presentation System Control Module, upon request, a current value of the Cumulative Rendition Period (a Renderer that is consistently used by the Presentation System in this fashion is referred to as a Timing Renderer).

As defined herein, Temporal Sequence Presentation Data, also referred to as Presentation Data, means data having the following characteristics: (a) the purpose, utility, or semantics of the data is closely associated with its presentation—presentation involves rendering of the data to achieve some effect (including but not limited to constituting a visible and/or audible presentation that can be monitored by a human being); (b) there are a plurality of rendering processes capable of effecting an appropriate presentation of the data; (c) the data comprises a set of elements; (d) each data element has a Rendition Type that corresponds to a type of Renderer that can be used to render the data element—some common Rendition Types are Pulse Code Modulation (PCM) audio, MPEG video, and JPEG images; (e) one or more Rendition Types may be Time-Distinguished Rendition Types—Time-Distinguished Rendition Types are Rendition Types of Temporal Sequence Presentation Data whose intrinsic characteristics and whose natural rendition process make them preferred candidates for defining and maintaining a system-wide Current Time parameter (note that most audio Rendition Types are Time-Distinguished Rendition Types); (f) associated with each element is a Data Time—the Data Time of some elements may be explicitly represented as part of the element (such elements are called Timestamped Elements), and the Data Time of some elements may be derivable only by performing or simulating an appropriate rendering process on all or part of the Presentation Data (such elements are called Sequential Elements); (g) the elements have a partial ordering, so that when performing rendering operations on the data it is possible to determine i) which data elements to deliver to the Renderers to begin the presentation process; and ii) given that the presentation process has reached a certain point, which data elements to deliver to the Renderers next to continue the presentation process; and (h) associated with each element is a Rendition Period—the Rendition Period is the length of time the rendering process should last for that element, where the Rendition Period of an element may be specified in many different ways, including but not limited to the following: (i) as a value explicitly stored as part of the element, (ii) as a fixed value associated with that type of data element, and stored in a header field of the Presentation Data, (iii) as a fixed value associated with a Presentation System, (iv) a difference between the Data Time of the element and the Data Time of a following element that would be submitted to the same Renderer in the course of presentation (i.e., the element is rendered until there is another element to be rendered by the same Renderer), (v) as a fixed property of the rendering process.

As defined herein, a Variable Rate Presentation (“VRP”) Module (also known as a VRP Module) means a module that: (a) accepts control commands and messages from the Presentation System; (b) maintains and, in response to commands from the Presentation System, updates the value of a Current Presentation Rate parameter where values of this parameter have the following interpretation: (i) a value of 1.0 means that presentation is to take place at the “normal” or default rate, (ii) a value less than 1.0 but greater than zero means that presentation is to take place slower than “normal” (the factor by which presentation is to be slowed down is equal to the inverse of the Current Presentation Rate value), (iii) a value greater than 1.0 means that presentation is to take place faster than “normal” (the factor by which presentation is to be sped up is equal to the Current Presentation Rate value), and (iv) a value less than zero is interpreted identically to the corresponding positive value of the parameter, but the direction of presentation is reversed (i.e., the presentation “runs in reverse”); (c) processes Temporal Sequence Presentation Data; (d) modifies Temporal Sequence Presentation Data in a manner consistent with the value of the Current Presentation Rate parameter and the Renderers to which the data will be later submitted, having the effect that the rate with which processing takes places will track the value of the Current Presentation Rate parameter. The implementation of Variable Rate Presentation may also involve one or more Renderers. In this case the value of the Current Presentation Rate parameter is attached to the data elements, or otherwise communicated to the appropriate Renderers.

In a Presentation System fabricated in accordance with one embodiment of the present invention, the Presentation System would maintain two separate values of the Current Time parameter. The first of the values would be a Current Data Time value that indicates the largest Data Time value of any data element that has already been submitted for rendering, or should have already been submitted for rendering. The second of the values would be a Current Presentation Time value, which would be the Cumulative Rendition Period of all data elements submitted since presentation began (i.e., the elapsed rendering time). In a Presentation System fabricated in accordance with another embodiment of the present invention, the Presentation System would maintain a single value of the Current Time parameter. Such an embodiment is typical of Presentation Systems that were not designed with the notion of variable rate playback in mind. More specifically, some such systems were designed with an implicit assumption that the only possible presentation rate was 1.0.

Presentation Time and Data Time are identical properties in traditional Presentation Systems, such as media players. However, when a Presentation System is enhanced with a Variable Rate Presentation (“VRP”) capability, these properties are no longer the same. We have discovered that this presents a problem when a traditional media player or other Presentation System is enhanced with a VRP capability, for two reasons. First, if a Presentation System Control Module only acquires a single Current Time value from a Timing Renderer, it is probably assuming that that value can be interpreted as both Current Data Time and Current Presentation Time. If these times are not equal, at least one of those assumptions will be in error. Secondly, if a single Current Time value is distributed to multiple components, some of which interpret the value as Current Data Time, and some of which interpret the value as Current Presentation Time, at least one of these interpretations will be in error. We have invented a way to convert Presentation Time to Data Time, and we have invented a method for reporting Presentation Time when only one time can be returned.

In accordance with one embodiment of the present invention, certain time-related properties (that will later be used to calculate Current Presentation Time and Current Data Time) are associated with Temporal Sequence Presentation Data elements by taking the following steps.

Step 1: from time to time as a user or some other controlling entity decides to change a rate of presentation, the Presentation System Control Module sends a message to a Variable Rate Presentation Module (VRP Module), specifying an updated value for a Current Presentation Rate parameter. When the VRP Module receives this message, it updates the value of its Current Presentation Rate parameter.

Step 2: in preparation for presentation, the Presentation System organizes Temporal Sequence Presentation Data elements (for example, audio samples) into collections called buffers.

Step 3: buffers are presented in an ordered or semi-order fashion for Presentation Rate modification and rendering, typically according to the Data Time of the first data element in a buffer.

Step 4: the number of unmodified samples in each buffer is determined, and the Unmodified Rendition Period of each element is obtained. The value of the Current Presentation Rate parameter is held constant (i.e., it is not allowed to change) while the VRP Module is processing a buffer. Also, the Rendition Period of all data elements in a buffer is constrained to be equal. Note, however, if it were desired to vary either the Current Presentation Rate or the Rendition Period within a buffer, that buffer could be broken down into multiple smaller buffers in which those properties were constant. In doing so, if necessary, each buffer could hold only a single data element.

Step 5: the Unmodified Cumulative Rendition Period for the buffer is calculated and retained as a property of the buffer by multiplying the Rendition Period of each data element in the buffer by the number of unmodified data elements in the buffer.

Step 6: the Data Time of the buffer is defined to be the Data Time associated with the first unmodified data element in the current buffer. The Data Time is acquired or calculated, and retained as a property of the buffer. If it is not directly specified as a property of the first data element of the current buffer, it can be calculated by adding the Data Time of the previous buffer to the Unmodified Cumulative Rendition Period of the previous buffer.

Step 7: the data elements in the current buffer are presentation rate modified, so that the ratio of the Cumulative Rendition Period of the buffer prior to presentation rate modification, divided by the Cumulative Rendition Period of the buffer following modification, is substantially equal to the Current Presentation Rate.

Step 8: the number of modified data elements in the modified buffer, and the Modified Rendition Period of each data element in the buffer, is determined and retained as a property of the buffer.

Step 9: the Modified Cumulative Rendition Period for the buffer is calculated and retained as a property of the buffer by multiplying the Modified Rendition Period of each data element in the buffer by the number of modified data elements in the buffer.

Step 10: the Modified Presentation Time of the buffer is defined to be the Presentation Time associated with the first modified data element in the buffer. This time is calculated and retained as a property of the buffer. It is calculated by adding to the Modified Presentation Time of the first modified data element of the previous buffer, the Modified Cumulative Rendition Time of the previous buffer.

Step 11: calculate, and retain as a property of the current buffer, the Cumulative Modified Data Element Count associated with the first data element in the current buffer by adding the Cumulative Modified Data Element Count associated with the first modified data element in the previous buffer to the number of modified data elements in the previous buffer.

Note that in this embodiment only the VRP Module needs to be informed of the current value of the Presentation Rate parameter. Renderer Modules, on the other hand, get all of their information about Presentation Rate from the buffer properties described above.

In accordance with one embodiment of the present invention, each Renderer is assumed to comprise a Core component. This Core component may be hardware, software, or a combination of hardware and software. For example, the Core component of an audio Renderer may be a Sound Card and its associated driver software. The Core component performs the essential rendering process for the particular Type of Temporal Sequence Presentation Data that the Renderer processes.

In accordance with one embodiment of the present invention, the Core component can be asked at any point in time to report the number of data elements rendered since a distinguished event such as, for example, an invocation of an Initialize or Clear command. Equivalently, the Core component rendering hardware or software may be able to report the number of milliseconds of rendering that has occurred since a distinguished event.

Renderers, especially Timing Renderers, must decide how to respond when other components of the Presentation System ask for the Current Time value without specifying whether Presentation Time or Data Time is desired. In many cases it is possible to determine that the Presentation System really wants to know what the Current Data Time is. Therefore in accordance with one embodiment of the present invention, a certain Data Time is returned when a request is made for the Current Time. For this, and other reasons, Renderers, especially Timing Renderers, must maintain an up-to-date and accurate value for both the Presentation Time and the Data Time associated with the data element currently being rendered. In accordance with one embodiment of the present invention, it is the Data Time of the data element currently being rendered by the Core component that is returned as the Current Time when the Current Time is requested by another module. Therefore, in accordance with one embodiment of the present invention, Current Presentation Time and Current Data Time are calculated by taking the following steps.

Step 1: a modified buffer with its associated properties as described above is submitted to an appropriate Renderer.

Step 2: if the Renderer's Core component is capable of reporting the number of milliseconds of rendering that has occurred since a distinguished event, and the Modified Presentation Time of this modified buffer is zero (or some other distinguished value), the Renderer triggers the distinguished event in its Core component.

Step 3: the Renderer submits the contents of the buffer to its Core component.

Step 4: the Renderer also stores each modified buffer in some method that allows ready access to all of the buffer properties until it has determined that all data elements in the buffer have been rendered.

Step 5: if the Core component is capable of reporting the number of data elements rendered since a distinguished event occurred, the Renderer calculates the Current Data Time and the Current Presentation Time using the following algorithm.

Step 5 a: it asks its Core component for the cumulative number of data elements rendered.

Step 5 b: it determines which buffer the next data element to be rendered will have come from, by identifying the particular buffer that has for its Cumulative Modified Data Element Count the largest cumulative sample number less than or equal to the reported number of data elements rendered—this buffer is referred to as the current rendering buffer.

Step 5 c: the current Data Time is equal to the Data Time of the current rendering buffer, plus an offset.

Step 5 d: the offset is calculated by multiplying the unmodified buffer duration by the Completion Fraction.

Step 5 e: the Completion Fraction is calculated by subtracting the cumulative sample number associated with the first sample in the current rendering buffer from the Core component's reported number, and dividing the result by the number of modified samples in the buffer.

Step 5 f: the Current Presentation Time is equal to the Modified Presentation Time of the current rendering buffer, plus an offset.

Step 5 g: the offset is calculated by multiplying the buffer's Modified Cumulative Rendition Period by the Completion Fraction.

Step 6: if the Core is capable of reporting the number of milliseconds of rendering that has occurred since a distinguished event, the Renderer calculates the Current Data Time and the Current Presentation Time using the following algorithm.

Step 6 a: it asks its Core component for the number of milliseconds of rendering that has occurred.

Step 6 b: it determines which buffer the next data element to be rendered will have come from by identifying the particular audio buffer that has for its Modified Presentation Time the largest value less than or equal to the Core's reported value—this buffer is referred to as the current rendering buffer.

Step 6 c: the current Data Time is equal to the Data Time of the current rendering buffer, plus an offset.

Step 6 d: the offset is calculated by multiplying the unmodified buffer duration by the Completion Fraction.

Step 6 e: the Completion Fraction is calculated by subtracting the Modified Presentation Time of the current rendering buffer from the Core component's reported value, and dividing the result by the Cumulative Modified Rendering Period of the buffer.

Step 6 f: the Current Presentation Time is equal to the Modified Presentation Time of the current rendering buffer, plus an offset.

Step 6 g: the offset is calculated by subtracting the Modified Presentation Time of the current rendering buffer from the Core component's reported value.

Step 6 h: the current Data Time is reported to the player as the Presentation Time.

Step 7: whenever an object requests the Current Time, the Renderer computes an updated value for the Presentation Time and Data Time, and reports either or both times as appropriate.

Let us define a temporal processing element as a sequence of Temporal Sequence Presentation Data samples over which the Current Presentation Rate does not change from one sample in the sequence to the next, and the default Rendition Period does not change from one sample in the sequence to the next. Such an element may comprise one or more data samples. Any sequence of Temporal Sequence Presentation Data samples can thus be considered to be organized into a sequence of temporal processing elements, each comprising one or more samples.

Referring to FIG. 3A, a flowchart is shown of a method 300 for identifying the values of various presentation-related parameters according to one embodiment of the present invention. Note that the steps illustrated in FIG. 3A need not be performed in the sequence illustrated. Furthermore, steps may be added to and/or removed from the method 300 illustrated in FIG. 3A to identify the values of desired properties.

The default period b_(d) of an element is the Rendition Period of such an element when it is rendered at normal speed. Thus b_(d) is the ratio of dτ, the change in Data Time, (which may be identified in step 302) and de, the change in the index E of the current element being rendered (which may be identified in step 304), as shown in Equation 1 (step 306).

b _(d) =dτ/de   Equation 1

The presentation rate r is equal to the ratio of dτ, the change in Data Time, and dt, the change in Presentation Time, (which may be identified in step 308), as shown in Equation 2 (step 310).

r=dτ/dt   Equation 2

The actual period b_(a) of an element is the Rendition Period of such an element when it is rendered at the current Presentation Rate. Thus b_(a) is the ratio of dt, the change in Presentation Time, and de, the change in the index E of the current element being rendered, as shown in Equation 3 (step 312).

b _(a) =dt/de=b _(d) /r   Equation 3

At any instant in the rendition of Temporal Sequence Presentation Data, the relationship between b_(d), b_(a), r, the element index E, the Data Time T_(D), and the Presentation Time T_(P), can be expressed in integral form. For a system in which the initial value of both Data Time and Presentation Time are zero before playback begins, the current Data Time T_(D) at Presentation Time T_(P) is given by Equation 4.

T_(D)=∫₀ ^(T) ^(P) dτ=∫₀ ^(T) ^(P) rdt   Equation 4

Therefore, the current Data Time T_(D) at Presentation Time T_(P) may be identified using the method 320 illustrated in FIG. 3B. The current Presentation Time T_(P) is identified (step 322) and the current Data Time T_(D) is identified either by integrating over dτ (step 324) or over rdt (step 326).

The current Data Time T_(D) at element index E is given by Equation 5:

T _(D)=∫₀ ^(E) dτ=∫ ₀ ^(E) rdt=∫ ₀ ^(E) r·b _(a) de=∫ ₀ ^(E) b _(d) de   Equation 5

Therefore, the current Data Time T_(D) at element index E may be identified using the method 330 illustrated in FIG. 3C. The current element index E is identified (step 332) and the current Data Time T_(D) is identified either by integrating over dτ (step 334), rdt (step 336), rb_(a)de (step 338) , or b_(d)de (step 339).

The current Presentation Time T_(P) at Data Time T_(D) is given by Equation 6.

T_(P)=∫₀ ^(T) ^(D) dt=∫₀ ^(T) ^(D) r¹dτ  Equation 6

Therefore, the current Presentation Time T_(P) at Data Time T_(D) may be identified using the method 340 illustrated in FIG. 3D. The current Data Time T_(D) is identified (step 342) and the current Presentation Time T_(P) is identified either by integrating over dt (step 344) or over r⁻¹dτ (step 346).

The current Presentation Time T_(P) at element index E is given by Equation 7.

T _(P)=∫₀ ^(E) dt=∫ ₀ ^(E) r ⁻¹ dτ=∫ ₀ ^(E)(b _(d) /r)de=∫ ₀ ^(E) b _(a) de   Equation 7

Therefore, the current Presentation Time T_(P) at element index E may be identified using the method 350 illustrated in FIG. 3E. The current element index E is identified (step 352) and the current Presentation Time T_(P) is identified either by integrating over dt (step 354), r⁻¹dτ (step 356), (b_(d)/r)de (step 358), or b_(a)de (step 359).

Those having ordinary skill in the art will understand how to add arbitrary constants to either the Data Time or Presentation Time calculations above to accommodate situations in which the initial values of those times are nonzero.

In one embodiment of a system in which Data Time and Presentation Time values may differ, each sample buffer is considered to be a temporal processing element. A Current Presentation Rate parameter r is associated with each such element. A Modified Cumulative Rendition Period b_(a), and an Unmodified Cumulative Rendition Period b_(d), is associated with each element.

Referring to FIG. 3F, a flowchart is shown of a method 360 that may be used in such an embodiment to identify the value of b_(d) for a particular element and for identifying the Data Time T_(D) at the beginning of the element. The Modified Cumulative Rendition Period b_(a) for the element is identified (step 362). The Current Presentation Rate r associated with the element is identified (step 364). The value of b_(d) for the element is identified as the product of b_(a) and r for that element (step 366). The Data Time T_(D) at the beginning of the element is identified as the sum of the values of b_(d) for all of the preceding elements (step 368). Note that the values of b_(d) for the preceding elements may be identified by iteratively applying steps 362-366 to those elements.

Referring to FIG. 3G, a flowchart is shown of a method 370 that may be used in such an embodiment to identify the value of b_(a) for a particular element and for identifying the Presentation Time T_(P) at the beginning of the element. The Unmodified Cumulative Rendition Period b_(d) for the element is identified (step 372). The Current Presentation Rate r associated with the element is identified (step 374). The value of b_(a) for the element is identified as the quotient of b_(d) and r for that element (step 376). The Presentation Time T_(P) at the beginning of the element is identified as the sum of the values of b_(a) for all of the preceding elements (step 378). Note that the values of b_(a) for the preceding elements may be identified by iteratively applying steps 372-376 to those elements.

It is not necessary to store both b_(d) and b_(a) for an element. Either value can be stored, and the other calculated from that stored value and the value of r for the element. Alternatively, the value of both b_(d) and b_(a) for an element may be stored, and r calculated as b_(d) divided by b_(a).

In one embodiment of a system in which Data Time and Presentation Time values may differ, the sequence of temporal processing elements that are rendered are assigned positive index values, so that the nth element rendered has index value n. A Current Presentation Rate parameter r_(n) is associated with the nth such element. A Modified Cumulative Rendition Period b_(a,n), and an Unmodified Cumulative Rendition Period b_(d,n), is associated with the nth element. The Presentation Time at the beginning of the nth element is T_(P,n), and the Data Time at the beginning of the nth element is T_(D,n). An Average Presentation Rate parameter R_(n) is associated with the nth element. This parameter is defined as shown in Equation 8:

R _(n) =T _(D,n) /T _(P,n)   Equation 8

In such an embodiment, the Data Time parameter T_(D,n) does not have to be explicitly maintained by the system, but instead may be calculated as needed as shown, for example, in Equation 9:

T _(D,n) =T _(P,n) ·R _(n)   Equation 9

Furthermore, R_(n), the value of the Average Rate parameter of the nth element, may be calculated without identifying the values of the Data Time parameter or the Unmodified Cumulative Rendition Period of any of the elements presented, as shown, for example, in Equation 10:

$\begin{matrix} {{R_{1} = 1}{R_{n} = {{\left( \frac{T_{P,{n - 1}}}{T_{P,n}} \right)R_{n - 1}} + {\left( \frac{b_{a,{n - 1}}}{T_{P,n}} \right){r_{n - 1}:\mspace{14mu} {{{for}\mspace{14mu} n} > 1}}}}}} & {{Equation}\mspace{14mu} 10} \end{matrix}$

Alternatively, the Presentation Time parameter T_(P,n) does not have to be explicitly maintained, but instead may be calculated as needed as shown in Equation 11:

T _(P,n) =T _(D,n) ·R _(n) ¹   Equation 11

In Equation 11, R_(n) ¹ is the inverse of the Average Rate parameter of the nth element. R_(n) ⁻¹ may be calculated without identifying the values of the Presentation Time parameter or the Modified Cumulative Rendition Period for any of the elements presented, as shown, for example, in Equation 12:

$\begin{matrix} {{R_{1}^{- 1} = 1}{R_{n}^{- 1} = {{\left( \frac{T_{D,{n - 1}}}{T_{D,n}} \right)R_{n - 1}^{- 1}} + {\left( \frac{b_{d,{n - 1}}}{T_{D,n}} \right){r_{n - 1}^{- 1}:\mspace{14mu} {{{for}\mspace{14mu} n} > 1}}}}}} & {{Equation}\mspace{14mu} 12} \end{matrix}$

When a component of a traditional player system that has been enhanced to support variable speed playback requests the value of the Current Time from a Timing Renderer (or other component capable of providing temporal information), several issues may be considered in order to return an appropriate value for the Current Time. The appropriate value for the Timing Renderer to return may differ from one request to another.

First, the Timing Renderer may determine whether to return a time value based on the current Data Time or a time value based on the current Presentation Time. In a traditional player, these two times are the same, but in a player capable of variable speed playback, or simply capable of differentiating between Data Time and Presentation Time, those two values are in general different. In some circumstances, it may be desirable to respond to a request for the Current Time with a time value that is based on the current Presentation Time. In other circumstances, however, it may be desirable to respond with a time value that is based on the current Data Time. The performance of the system is enhanced, therefore, in various embodiments of the present invention by enabling the Timing Renderer to return a time value that is derived from an appropriate one of the current Data Time and current Presentation time, based on the circumstances.

Moreover, it is commonly the case that the requesting component will either add an offset to the time returned, thus in effect calculating an earlier or later time, or subtract the time returned from another time, thus in effect calculating a temporal differential. In many cases the function performed by such an addition or subtraction is such that the calculated time or temporal differential would benefit from being adjusted by taking into account the current presentation rate, or some value determined by the course of previous or future variations in presentation rate. But because the requesting component is not aware that playback speeds are variable, it does not make such an adjustment.

In summary, in various embodiments of the present invention in which a traditional player system is enhanced to support variable speed playback, the performance of the system may be improved by ensuring that the Timing Renderer determines whether to base the time value returned on the Current Presentation Time or the Current Data Time when a component asks for the Current Time. Furthermore, in various embodiments of the present invention, the time returned is adjusted to take into account the current presentation rate, or a sequence of variations in presentation rates, to further improve system performance.

In general, an advantageous strategy for the Timing Renderer to employ in responding to an ambiguous request for the Current Time is to identify which of a number of known “time value request cases” the current request is an instance and, based on this identification, to select an algorithm to use to calculate an appropriate time value to return. In general an appropriate time value algorithm may make use of a base time and a set of algorithm-specific parameters whose values the Timing Renderer may identify on a case-by-case base. This strategy is shown in a flow chart in FIG. 4.

The Timing Renderer receives a request for a Current Time value (step 402). The Timing Renderer identifies relevant characteristics of the timing request (referred to herein as the “distinguishing signature” of the request) (step 404). The Timing Render identifies the known time value request case of which the current request is an instance (step 406).

The Timing Renderer selects, based on the identified distinguishing signature and request case, an algorithm to use to calculate an appropriate time value to return (step 408). The Timing Renderer identifies an appropriate time value base and parameters for use with the identified algorithm based on the distinguishing signature and request case (step 410). The Timing Renderer uses the identified algorithm, base, and parameters to calculate a time value (step 412). The Timing Renderer returns the time value identified in step 412 to the requesting component (step 414).

In one set of cases, the appropriate base time will always be either the Current Data Time or the Current Presentation Time, and there will be two relevant parameters: an incorrect offset (or differential) that the Timing Renderer anticipates the requesting component will add (or compute), and a correct offset (or differential) that the Timing Renderer anticipates that the requesting component intends to add (or compute). Frequently, the requesting component will employ an incorrect offset, or incorrectly calculate a differential, when the Current Time on which it is basing its calculation is the Data Time (Presentation Time), and the offset it intends to add, or differential it intends to calculate, is intrinsically the Presentation Time (Data Time).

In these cases, an advantageous method 500 for the Timing Renderer to employ in responding to the request is illustrated by the flowchart shown in FIG. 5. In general, in the method 500 the Timing Renderer determines, from the distinguishing signature of the request, which one of a number of standard time value request cases the current request is an instance of. Then, based on the identification of the time value request case, the Timing Renderer:

-   -   (A) selects either the current Data Time or the current         Presentation Time as the correct base time;     -   (B) determines whether it is anticipated that the requesting         component will add an incorrect offset to the time value         returned, or calculate an erroneous differential from the time         returned; and, if so,     -   (C) adds to the base time value the correct offset or         differential that the Timing Renderer anticipates, based on the         request signature, that the requesting component intends to add         or compute; and     -   (D) subtracts from the base value the incorrect offset or         differential that the Timing Renderer anticipates, based on the         request signature, that the requesting component will actually         add or compute.

More specifically, the method 500 determines whether the distinguishing request signature signals a custom time value request case (step 502). In one embodiment of the present invention, cases not falling within one of the set of cases described below with respect to steps 514, 516, 520, 522, 528, 530, 534, and 536 are regarded as custom cases for which custom time value calculation algorithms and parameters to perform those algorithms are identified on a case-by-case basis (step 504).

If the distinguishing request signature does not signal a custom time value request case, the method 500 determines whether the signature identifies a Presentation Time-based timing request (step 506). If the distinguishing request signature does identify a Presentation Time-based timing request, the method 500 uses Presentation Time as a base time. The method 500 determines whether the distinguishing request signature identifies a comparison-type timing request (step 508).

If the distinguishing request signature identifies a comparison-type timing request, the method 500 determines whether the intent of the calculation that the requesting component is expected to perform is to determine a Presentation Time differential Δ_(P) (step 510). If the requested component intends to calculate a Presentation Time differential, then the method 500 identifies the current case as the “PCP” case (step 514). The meaning of this case and other cases will be described in more detail below. If the intent of the calculation that the requesting component is expected to perform is to determine a Data Time differential Δ_(D), then the method 500 identifies the current case as the “PCD” case (step 516).

If the distinguishing request signature does not identify a comparison-type timing request, the method 500 determines whether the requesting component is expected to calculate a Presentation Time offset O_(P) (step 518). If the requesting component is expected to calculate a Presentation Time offset, then the method 500 identifies the current case as the “POP” case (step 520). If the requesting component is not expected to calculate a Presentation Time offset, then the method 500 identifies the current case as the “POD” case (step 522).

Returning to step 506, if the distinguishing request signature does not identify a Presentation Time-based timing request, the method 500 uses Data Time as a base time. The method 500 determines whether the distinguishing request signature identifies a comparison-type timing request (step 524). If the distinguishing request signature identifies a comparison-type timing request, the method 500 determines whether the intent of the calculation that the requesting component is expected to perform is to determine a Data Time differential Δ_(D) (step 526). If the requesting component intends to calculate a Data Time differential, then the method 500 identifies the current case as the “DCD” case (step 528). If the intent of the calculation that the requesting component is expected to perform is to determine a Presentation Time differential Δ_(P), the method 500 identifies the current case as the “DCP” case (step 530).

Returning to step 524, if the distinguishing request signature does not identify a comparison-type timing request, the method 500 determines whether the requesting component is expected to calculate a Data Time offset O_(D) (step 532). If the requesting component intends to calculate a Data Time offset, then the method 500 identifies the current case as the “DOD” case (step 534). If the requesting component intends to calculate a Presentation Time offset, then the method 500 identifies the current case as the “DOP” case (step 536).

For example, suppose that the requesting component is attempting to determine what the value of the Presentation Time was when the Data Time was 2.5 seconds earlier than the current moment. Further suppose that it determines this value by requesting the current time, and subtracting 2.5 seconds from the value returned. Consider the case in which the Presentation Rate r is now 2.0 (signifying a playback rate that is twice the default or normal playback rate), and has had that value for the past minute. Then the optimal value for the Timing Renderer to return is a value that is based on the Presentation Time. Further, the optimal value for the Timing Renderer to return (in seconds) is given by Equation 13.

T _(O) =T _(P)+(−2.5/r)−(−2.5)   Equation 13

If the Timing Renderer returns T_(O), and the requesting component adds an offset of (−2.5 seconds), the final number calculated will be given by Equation 14, which results in the desired value.

T _(F) =T _(O)−2.5=T _(P)+(−2.5/r)−(−2.5)+(−2.5)=T _(P)+(−2.5)/r   Equation 14

In all of the cases mentioned above with respect to steps 514, 516, 520, 522, 528, 530, 534, and 536, three values are identified: a base time, a “right” offset, and a “wrong” offset. The “right” offset is an offset that, when added to the base time, returns an appropriate time value to return in response to the time request received by the Timing Renderer. The “wrong” offset is an offset that the Timing Renderer expects the requesting component to add to the time value returned by the Timing Renderer. To compensate for this expected “wrong” offset, the Timing Renderer returns a time value that is equal to the base time plus the right offset minus the wrong offset (step 538). If the requesting component adds the wrong offset to the returned value, as expected, the resulting value will be equal to the base time plus the right offset, which is the desired time value in response to the request.

For example, in the “DOP” case (step 536) the value desired by the requesting component when the Current Time is requested is the current Data Time, and the requesting component will intend to add a “right” Presentation Time offset O_(P) to the value returned, but, it is anticipated, will add a “wrong” Data Time offset O_(D). In this case, in one embodiment the Timing Renderer returns the current Data Time, plus the right offset O_(P), minus the wrong offset O_(D).

In the “DOD” case (step 534), the value desired by the requesting component when the Current Time is requested is the current Data Time, and the requesting component will intend to add a “right” Data Time offset O_(D) to the value returned, and, it is anticipated, will actually add the proper offset. In this case, the in one embodiment the Timing Renderer returns the current Data Time, without any adjustment.

In the “DCP” case (step 530), the value desired by the requesting component when the Current Time is requested is the current Data Time, and the requesting component will compare the time returned with another Data Time value that differs by an amount Δ_(D), and, it is anticipated, will interpret the difference between those two values as Presentation Time differential Δ_(P). In this case, in one embodiment the Timing Renderer returns the current Data Time, plus the right differential Δ_(P), minus the wrong differential Δ_(D).

In the “DCD” case (step 528), the value desired by the requesting component when the Current Time is requested is the current Data Time, and the requesting component will compare the time returned with another Data Time value that differs by an amount Δ_(D), and, it is anticipated, will correctly interpret the difference between those two values as a Data Time differential. In this case, in one embodiment the Timing Renderer returns the current Data Time, without any adjustment.

In the “POP” case (step 520), the value desired by the requesting component when the Current Time is requested is the current Presentation Time, and the requesting component will intend to add a “right” Presentation Time offset O_(P) to the value returned, and, it is anticipated, will actually add the proper offset. In this case, in one embodiment the Timing Renderer returns the current Presentation Time, without any adjustment.

In the “POD” case (step 522), the value desired by the requesting component when the Current Time is requested is the current Presentation Time, and the requesting component will intend to add a “right” Data Time offset O_(D) to the value returned, but, it is anticipated, will add a “wrong” Presentation Time offset O_(P). In this case, in one embodiment the Timing Renderer returns the current Presentation Time, plus the right offset O_(D), minus the wrong offset O_(P).

In the “PCD” case (step 516), the value desired by the requesting component when the Current Time is requested is the current Presentation Time, and the requesting component will compare the time returned with another Presentation Time value that differs by an amount Δ_(P), and, it is anticipated, will interpret the difference between those two values as Data Time differential Δ_(D). In this case, in one embodiment the Timing Renderer returns the current Presentation Time, plus the right differential Δ_(D), minus the wrong differential Δ_(P).

In the “PCP” case (step 514), the value desired by the requesting component when the Current Time is requested is the current Presentation Time, and the requesting component will compare the time returned with another Presentation Time value that differs by an amount Δ_(P), and, it is anticipated, will correctly interpret the difference between those two values as a Presentation Time differential. In this case, in one embodiment the Timing Renderer returns the current Presentation Time, without any adjustment.

In all cases for which the Timing Renderer calculates an offset or differential, any of the techniques discussed above for converting Data Times to Presentation Times, or Presentation Times to Data Times, may be employed as appropriate. In some cases the Timing Renderer may be able to predict that a requesting component will later attempt to identify the Data Time or Presentation Time associated with a moment that the Timing Renderer can identify. The Timing Renderer may choose to store either or both of the identified moment's Data Time and Presentation Time, and will be able to employ those stored times directly in computing a later “right” offset and “wrong” offset.

In some cases the values of O_(P), O_(D), Δ_(P), or Δ_(D) that a Timing Renderer might identify for a timing value request may not be equal to the actual values that the requesting component might employ following the request. It is frequently the case in engineered systems that exact values cannot be determined precisely, and components must use estimates of values. The values of O_(P), O_(D), Δ_(P), or Δ_(D) may be estimated using any appropriate techniques, including those that are well-known to those having ordinary skill in the art.

As indicated above with respect to FIGS. 4-5, whenever a Timing Renderer receives a request for the Current Time, the Timing Renderer may determine which of the time value request cases this is an instance of, so as to be able to return an appropriate time value. The Timing Renderer may, for example, determine which case this request is an instance of by identifying a distinguishing signature associated with the current request, and using the distinguishing signature to identify a corresponding time value request case. Once the Timing Renderer has identified the corresponding time value request case, it may employ that identification to determine whether to base the return value on Data Time or Presentation Time. The Timing Renderer may also use the request case identification to determine how to adjust the selected base time. For instance, the Timing Renderer may base its estimate of O_(P), O_(D), Δ_(P), or Δ_(D) on the request signature and/or the request case.

The distinguishing signature may be identified from one or more properties of the request itself. In addition, properties related to the state of the player or other properties of the rendering system that are accessible to the Timing Renderer may contribute to the signature. The distinguishing signature may be an arbitrary combination of many properties, including but not limited to one or more of the following:

-   -   The return address of the subroutine call from the requesting         component to the Timing Renderer (if the request is made via a         subroutine call), or more generally a pattern present in the         stack frame of the calling process or thread (for example the         return address of the third subroutine back in the stack frame);     -   The specific subclass of the Timing Renderer through which the         requesting component makes its request (in the case of an         object-oriented request);     -   The identity of the message by which the timing request is made,         if a message-passing protocol is used to make the timing         request;     -   The identity of the execution thread or process within which the         request is being made;     -   The phase, stage, or state of the player thread, process, or         application when the timing request is made;     -   A distinguished or relevant pattern in the player memory;     -   A preference value set by the user or an external monitor         program or tuning algorithm;     -   The number, timing, or specific pattern of prior calls to the         Timing Renderer;     -   The name, source, encoding format, or other characteristic of         the data currently being rendered;     -   The name of the program being executed, the user's name, or the         identity or make of the computer on which the program is being         executed;     -   A value accessible over the Internet, located in the memory of         the computer running the player program, present on a hard disk         or other data storage device, or otherwise directly or         indirectly accessible to the Timing Renderer;     -   The state of a button, lever, slider, switch, or other input         device directly or indirectly accessible to the Timing Renderer;     -   The hardware characteristics of the platform on which the         program is running, including but not limited to the size of         memory, the identity or characteristics of the processor, or the         size of external storage; and     -   The source of the data being rendered, or the nature of the         channel between the data source and the player. For instance, in         the case of media streaming over the Internet, the URL of the         source material, or the capacity of the Internet connection, may         constitute a factor.

Note that the term “property of the request” refers herein to any property from which the distinguishing signature of the request is derived. As the examples above indicate, such properties need not be represented in the request itself. For example, the state of any part of the rendering system may be treated as a “property of the request” for purposes of identifying the distinguishing signature of the request. The determination of the properties which comprise the distinguishing signature from which the time value request case is identified, and the determination of the time value parameters from which the final time value is calculated, may be accomplished in multiple ways, including but not limited to the following:

-   -   Examining the source code of the player program;     -   Analyzing the operating characteristics of the player program         when playing media at various speeds;     -   Analyzing debugging output, error messages, and performance logs         generated by the player program;     -   Providing a user interface by which users of the program may         identify the properties which distinguish one request case from         another, and by which users may specify the values of the time         value parameters to be used with each request case;     -   Implementing an automatic optimization technique for traversing         the search space of possible distinguishing properties and         parameter values, identifying a metric for determining a         goodness-of-fit value for each point in the search space, and         running an optimization algorithm for identifying the best         location in the search space.

Using any of the techniques above, or others that will occur to persons of ordinary skill in the art, a specification may be determined of relevant properties that together form a distinguishing request signature. The request signature then provides the mapping to a corresponding timing request case, and constitutes the means by which a corresponding set of time value parameters may be identified. The time value request case identity and the time value parameters together determine and fully specify the corresponding time value for the Timing Renderer to calculate and to return to the requesting component.

It is to be understood that although the invention has been described above in terms of particular embodiments, the foregoing embodiments are provided as illustrative only, and do not limit or define the scope of the invention. Various other embodiments, including but not limited to the following, are also within the scope of the claims. For example, elements and components described herein may be further divided into additional components or joined together to form fewer components for performing the same functions.

The techniques described above may be implemented, for example, in hardware, software, firmware, or any combination thereof. The techniques described above may be implemented in one or more computer programs executing on a programmable computer including a processor, a storage medium readable by the processor (including, for example, volatile and non-volatile memory and/or storage elements), at least one input device, and at least one output device. Program code may be applied to input entered using the input device to perform the functions described and to generate output. The output may be provided to one or more output devices.

Each computer program within the scope of the claims below may be implemented in any programming language, such as assembly language, machine language, a high-level procedural programming language, or an object-oriented programming language. The programming language may, for example, be a compiled or interpreted programming language.

Each such computer program may be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a computer processor. Method steps of the invention may be performed by a computer processor executing a program tangibly embodied on a computer-readable medium to perform functions of the invention by operating on input and generating output. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, the processor receives instructions and data from a read-only memory and/or a random access memory. Storage devices suitable for tangibly embodying computer program instructions include, for example, all forms of non-volatile memory, such as semiconductor memory devices, including EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROMs. Any of the foregoing may be supplemented by, or incorporated in, specially-designed ASICs (application-specific integrated circuits) or FPGAs (Field-Programmable Gate Arrays). A computer can generally also receive programs and data from a storage medium such as an internal disk (not shown) or a removable disk. These elements will also be found in a conventional desktop or workstation computer as well as other computers suitable for executing computer programs implementing the methods described herein, which may be used in conjunction with any digital print engine or marking engine, display monitor, or other raster output device capable of producing color or gray scale pixels on paper, film, display screen, or other output medium. 

What is claimed is:
 1. A method for use in a rendering system for rendering temporal sequence presentation data, the method comprising steps of: (A) initializing a presentation time parameter value to zero, the presentation time parameter representing an amount of time elapsed during rendering of a portion of the temporal sequence presentation data; (B) for each element in the portion of the temporal sequence presentation data; (1) identifying a default rendition period of the element; (2) identifying an actual presentation rate of the element; (3) dividing the default rendition period of the element by the actual presentation rate of the element; (4) adding the quotient of step (3) to the presentation time parameter value; and (C) identifying the sum produced by steps (A) and (B) as the presentation time parameter value.
 2. A device for use in a rendering system for rendering temporal sequence presentation data, the device comprising: initialization means for initializing a presentation time parameter value to zero, the presentation time parameter representing an amount of time elapsed during rendering of a portion of the temporal sequence presentation data; iteration means for each element in the portion of the temporal sequence presentation data, the iteration means comprising: first identification means for identifying a default rendition period of the element; second identification means for identifying an actual presentation rate of the element; division means for dividing the default rendition period of the element by the actual presentation rate of the element; summing means for adding the quotient produced by the division means to the presentation time parameter value; and third identification means for identifying the sum produced by the initialization means and the iteration means as the presentation time parameter value.
 3. A method for use in a rendering system for rendering temporal sequence presentation data, the method comprising steps of: (A) receiving an explicit request for a value of a presentation time parameter representing an amount of time elapsed during rendering of a portion of the temporal sequence presentation data, wherein the amount of time differs from an amount of time required to render the portion of the temporal sequence presentation data at a default presentation rate; and (B) providing the value of the presentation time parameter in response to the request.
 4. A device for use in a rendering system for rendering temporal sequence presentation data, the device comprising: means for receiving an explicit request for a value of a presentation time parameter representing an amount of time elapsed during rendering of a portion of the temporal sequence presentation data, wherein the amount of time differs from an amount of time required to render the portion of the temporal sequence presentation data at a default presentation rate; and means for providing the value of the presentation time parameter in response to the request.
 5. A method for use in a rendering system for rendering temporal sequence presentation data, the method comprising steps of: (A) receiving an explicit request for the value of a data time parameter representing an amount of time required to render a portion of the temporal sequence presentation data at a default presentation rate, wherein the amount of time differs from an amount of time elapsed during rendering of the portion of the temporal sequence presentation data; and (B) providing the value of the data time parameter in response to the request.
 6. A device for use in a rendering system for rendering temporal sequence presentation data, the device comprising: means for receiving an explicit request for the value of a data time parameter representing an amount of time required to render a portion of the temporal sequence presentation data at a default presentation rate, wherein the amount of time differs from an amount of time elapsed during rendering of the portion of the temporal sequence presentation data; and means for providing the value of the data time parameter in response to the request.
 7. A method for enhancing a rendering system which renders temporal sequence presentation data, the rendering system not including distinct current presentation time and current data time parameters, the method comprising steps of: (A) adding to the rendering system a monitoring module for monitoring values of a current presentation rate parameter that may vary over time, the current presentation rate parameter representing a current rate at which the portion of the temporal sequence presentation data is being rendered; and (B) adding to the rendering system a data time module to identify, based on the values of the current presentation rate parameter, a current data time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at a default presentation rate.
 8. The method of claim 7, further comprising a step of: (C) adding to the rendering system a presentation rate modification module to render a portion of the temporal sequence presentation data at any of a plurality of presentation rates.
 9. The method of claim 7, further comprising a step of: (C) adding to the rendering system a current time module for returning the value of a predetermined one of the presentation time parameter and the data time parameter in response to a request for a current time.
 10. The method of claim 7, wherein the presentation time parameter has a value that differs from the data time parameter value.
 11. A method for enhancing a rendering system which renders temporal sequence presentation data, the rendering system not including distinct current presentation time and current data time parameters, the method comprising steps of: (A) adding to the rendering system a monitoring module for monitoring values of a current presentation rate parameter that may vary over time, the current presentation rate parameter representing a current rate at which the portion of the temporal sequence presentation data is being rendered; (B) adding to the rendering system a data time module to identify, based on the values of the current presentation rate parameter, a current data time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at a default presentation rate; (C) adding to the rendering system a presentation rate modification module to render a portion of the temporal sequence presentation data at any of a plurality of presentation rates; and (D) adding to the rendering system a current time module for returning the value of a predetermined one of the presentation time parameter and the data time parameter in response to a request for a current time; wherein the presentation time parameter has a value that differs from the data time parameter value.
 12. A system comprising: a rendering system which renders temporal sequence presentation data, the rendering system not including distinct current presentation time and current data time parameters; a monitoring module for monitoring values of a current presentation rate parameter that may vary over time, the current presentation rate parameter representing a current rate at which the portion of the temporal sequence presentation data is being rendered; and a data time module to identify, based on the values of the current presentation rate parameter, a current data time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at a default presentation rate; wherein the presentation time parameter has a value that differs from the data time parameter value.
 13. The system of claim 12, further comprising: a presentation rate modification module to render a portion of the temporal sequence presentation data at any of a plurality of presentation rates.
 14. The system of claim 12, further comprising: a current time module for returning the value of a predetermined one of the presentation time parameter and the data time parameter in response to a request for a current time.
 15. A system comprising: a rendering system which renders temporal sequence presentation data, the rendering system not including distinct current presentation time and current data time parameters: a monitoring module for monitoring values of a current presentation rate parameter that may vary over time, the current presentation rate parameter representing a current rate at which the portion of the temporal sequence presentation data is being rendered; a data time module to identify, based on the values of the current presentation rate parameter, a current data time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at a default presentation rate; a presentation rate modification module to render a portion of the temporal sequence presentation data at any of a plurality of presentation rates; and a current time module for returning the value of a predetermined one of the presentation time parameter and the data time parameter in response to a request for a current time; wherein the presentation time parameter has a value that differs from the data time parameter value.
 16. A method for enhancing a rendering system which renders temporal sequence presentation data, the rendering system not including distinct current presentation time and current data time parameters, the method comprising steps of: (A) adding to the rendering system a monitoring module for monitoring values of a current presentation rate parameter that may vary over time, the current presentation rate parameter representing a current rate at which the portion of the temporal sequence presentation data is being rendered; and (B) adding to the rendering system a presentation time module to identify, based on the values of the current presentation rate parameter, a current presentation time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at the current rate; wherein the presentation time parameter has a value that differs from the data time parameter value.
 17. The method of claim 16, further comprising a step of: (C) adding to the rendering system a presentation rate modification module to render a portion of the temporal sequence presentation data at any of a plurality of presentation rates.
 18. The method of claim 16, further comprising a step of: (C) adding to the rendering system a current time module for returning the value of a predetermined one of the presentation time parameter and the data time parameter in response to a request for a current time.
 19. A method for enhancing a rendering system which renders temporal sequence presentation data, the rendering system not including distinct current presentation time and current data time parameters, the method comprising steps of: (A) adding to the rendering system a monitoring module for monitoring values of a current presentation rate parameter that may vary over time, the current presentation rate parameter representing a current rate at which the portion of the temporal sequence presentation data is being rendered; (B) adding to the rendering system a presentation time module to identify, based on the values of the current presentation rate parameter, a current presentation time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at the current rate; (C) adding to the rendering system a presentation rate modification module to render a portion of the temporal sequence presentation data at any of a plurality of presentation rates; and (D) adding to the rendering system a current time module for returning the value of a predetermined one of the presentation time parameter and the data time parameter in response to a request for a current time; wherein the presentation time parameter has a value that differs from the data time parameter value.
 20. A system comprising: a rendering system which renders temporal sequence presentation data, the rendering system not including distinct current presentation time and current data time parameters; a monitoring module for monitoring values of a current presentation rate parameter that may vary over time, the current presentation rate parameter representing a current rate at which the portion of the temporal sequence presentation data is being rendered; and a presentation time module to identify, based on the values of the current presentation rate parameter, a current presentation time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at the current rate; wherein the presentation time parameter has a value that differs from the data time parameter value.
 21. The system of claim 20, further comprising: a presentation rate modification module to render a portion of the temporal sequence presentation data at any of a plurality of presentation rates.
 22. The system of claim 20, further comprising: a current time module for returning the value of a predetermined one of the presentation time parameter and the data time parameter in response to a request for a current time.
 23. A system for enhancing a rendering system which renders temporal sequence presentation data, the rendering system not including distinct current presentation time and current data time parameters, the system comprising: a monitoring module for monitoring values of a current presentation rate parameter that may vary over time, the current presentation rate parameter representing a current rate at which the portion of the temporal sequence presentation data is being rendered; a presentation time module to identify, based on the values of the current presentation rate parameter, a current presentation time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at the current rate; a presentation rate modification module to render a portion of the temporal sequence presentation data at any of a plurality of presentation rates; and a current time module for returning the value of a predetermined one of the presentation time parameter and the data time parameter in response to a request for a current time; wherein the presentation time parameter has a value that differs from the data time parameter value.
 24. A method for use in conjunction with a rendering system which renders temporal sequence presentation data, the method comprising steps of: (A) receiving a request for a current time of the temporal sequence presentation data after a portion of the temporal sequence presentation data has been rendered by the rendering system; (B) in response to the request, performing steps of: (1) identifying a data time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at a default presentation rate; and (2) providing the data time parameter value in response to the request.
 25. The method of claim 24, wherein the step (B) comprises steps of: (B)(1)(a) identifying a number of elements in the portion of the temporal sequence presentation data; (B)(1)(b) identifying a rendition period required to render one of the elements in the portion of the temporal sequence presentation data; and (B)(1)(c) multiplying the number of elements by the identified rendition period to identify the value of the data time parameter.
 26. The method of claim 24, wherein the step (B) comprises steps of: (B)(1)(a) initializing the data time parameter value to zero; (B)(1)(b) for each element in the portion of the temporal sequence presentation data: (i) identifying a default rendition period of the element; (ii) adding the default rendition period to the data time parameter value; and (B)(2) providing the sum produced by steps (B)(1)(a) and (B)(1)(b) as the data time parameter value.
 27. The method of claim 24, wherein the step (B) comprises steps of: (B)(1)(a) initializing the data time parameter value to zero; (B)(1)(b) for each element in the portion of the temporal sequence presentation data: (i) identifying an actual rendition period of the element; (ii) identifying an actual presentation rate of the element; (iii) multiplying the actual rendition period of the element by the actual presentation rate of the element; (iv) adding the product of step (c) to the data time parameter value; and (B)(2) providing the sum produced by steps (B)(1)(a) and (B)(1)(b) as the data time parameter value.
 28. The method of claim 24, wherein the step (B) comprises a step of identifying, as the value of the data time parameter, a time integral of a presentation rate of the portion over the amount of time elapsed during rendering of the portion, wherein the presentation rate is equal to the ratio of a change in the value of the data time parameter over time to a change in the value of the presentation time parameter over time.
 29. A device for use in conjunction with a rendering system which renders temporal sequence presentation data, the device comprising: means for receiving a request for a current time of the temporal sequence presentation data after a portion of the temporal sequence presentation data has been rendered by the rendering system; response means activated by receipt of the request, the response means comprising: means for identifying a data time parameter value representing an amount of time required to render the portion of the temporal sequence presentation data at a default presentation rate; and means for providing the data time parameter value in response to the request.
 30. A method for use in conjunction with a rendering system which renders temporal sequence presentation data, the method comprising steps of: (A) receiving a request for a current time of the temporal sequence presentation data after a portion of the temporal sequence presentation data has been rendered by the rendering system; (B) determining, based on a property of the request, whether to return a value of a data time parameter or a value of a presentation time parameter; and (C) returning, in response to the request, the value determined in step (B).
 31. The method of claim 30, wherein the property comprises an property of an executing computer program which submitted the request.
 32. The method of claim 30, wherein the property comprises a property of a computer platform on which the method is executing.
 33. The method of claim 30, wherein the property comprises a value accessible to the method during step (B).
 34. A device for use in conjunction with a rendering system which renders temporal sequence presentation data, the device comprising: means for receiving a request for a current time of the temporal sequence presentation data after a portion of the temporal sequence presentation data has been rendered by the rendering system; means for determining, based on a property of the request, whether to return a value of a data time parameter or a value of a presentation time parameter; and means for returning, in response to the request, the value determined by the means for determining.
 35. A method for use in conjunction with a rendering system which renders temporal sequence presentation data, the method comprising steps of: (A) receiving a request for a current time of the temporal sequence presentation data after a portion of the temporal sequence presentation data has been rendered by the rendering system; (B) identifying an initial current time of the temporal sequence presentation data; (C) identifying at least one presentation rate associated with the temporal sequence presentation data; (D) modifying the initial current time based on the identified at least one presentation rate to produce a modified current time; and (E) providing the modified current time in response to the request.
 36. The method of claim 35, wherein step (B) comprises a step of identifying a presentation time of the temporal sequence presentation data.
 37. The method of claim 35, wherein step (B) comprises a step of identifying a data time of the temporal sequence presentation data.
 38. The method of claim 35, wherein step (C) comprises a step of identifying a current presentation rate of the temporal sequence presentation data.
 39. The method of claim 35, wherein step (C) comprises a step of identifying a presentation rate of the temporal sequence presentation data during rendering of the portion of the temporal sequence presentation data by the rendering system.
 40. The method of claim 35, wherein step (D) comprises a step of adding to the initial current time a value that is proportional to the identified presentation rate.
 41. The method of claim 35, wherein step (D) comprises a step of subtracting from the initial current time a value that is proportional to the identified presentation rate.
 42. The method of claim 35, wherein the step (A) comprises a step of receiving the request from a requesting component, and wherein the step (D) comprises steps of: (D)(1) identifying a first offset expected to be added by the requesting component to the modified current time; (D)(2) identifying a second offset based on the identified at least one presentation rate; (D)(3) adding the second offset to the initial current time to produce an intermediate current time; and (D)(4) subtracting the first offset from the intermediate current time to produce the modified current time.
 43. A device for use in conjunction with a rendering system which renders temporal sequence presentation data, the device comprising: means for receiving a request for a current time of the temporal sequence presentation data after a portion of the temporal sequence presentation data has been rendered by the rendering system; means for identifying an initial current time of the temporal sequence presentation data; means for identifying at least one presentation rate associated with the temporal sequence presentation data; means for modifying the initial current time based on the identified at least one presentation rate to produce a modified current time; and means for providing the modified current time in response to the request.
 44. A method for use in conjunction with a rendering system which renders temporal sequence presentation data including a plurality of data samples, the method comprising steps of: (A) grouping the plurality of data samples into a plurality of buffers; (B) associating with each of the plurality of buffers a corresponding presentation rate; (C) associating with each of the plurality of buffers a corresponding initial data time; (D) associating with each of the plurality of buffers a corresponding initial presentation time; (E) associating with each of the plurality of buffers a default rendition period; and (F) associating with each of the plurality of buffers an actual rendition period.
 45. The method of claim 44, wherein the plurality of buffers is logically arranged in an ordered sequence, and wherein the step (C) comprises steps of, for each of the plurality of buffers: (C)(1) identifying the initial data time associated with the previous buffer in the ordered sequence; (C)(2) identifying the default rendition period of the previous buffer in the ordered sequence; and (C)(3) identifying the initial data time of the buffer as the sum of the initial data time identified in step (C)(1) and the default rendition period identified in step (C)(2).
 46. The method of claim 45, wherein the plurality of buffers is logically arranged in an ordered sequence, and wherein the step (D) comprises steps of, for each of the plurality of buffers: (D)(1) identifying the initial presentation time associated with the previous buffer in the ordered sequence; (D)(2) identifying the actual rendition period of the previous buffer in the ordered sequence; and (D)(3) identifying the initial presentation time of the buffer as the sum of the initial presentation time identified in step (D)(1) and the actual rendition period identified in step (D)(2).
 47. The method of claim 45, wherein the plurality of buffers is logically arranged in an ordered sequence, and wherein the step (F) comprises steps of, for each of the plurality of buffers: (F)(1) identifying the number of samples in the buffer; (F)(2) identifying the default rendition period of a sample in the buffer; and (F)(3) identifying the actual rendition period of the buffer as the product of the identified number of samples times the identified default rendition period of a sample in the buffer.
 48. A device for use in conjunction with a rendering system which renders temporal sequence presentation data including a plurality of data samples, the device comprising: grouping means for grouping the plurality of data samples into a plurality of buffers; first association means for associating with each of the plurality of buffers a corresponding presentation rate; second association means for associating with each of the plurality of buffers a corresponding initial data time; third association means for associating with each of the plurality of buffers a corresponding initial presentation time; fourth association means for associating with each of the plurality of buffers a default rendition period; and fifth association means for associating with each of the plurality of buffers an actual rendition period. 